Packing Disordered Molecular Crystals and their Molecular Alloys

Tamarit, J. Ll.; López, D. O.; Haget, Y.

doi:10.1107/s0021889896012228

Cited by 19 publications

(15 citation statements)

References 6 publications

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“…0.57) when compared to other plastic phases for which the existence of dynamical hydrogen bonds has been clearly demonstrated. 62,63 As for the low-temperature phase for all these compounds, the a lattice parameter changes faster than b and c with temperature ( Figure 2) because the nearest neighbors molecules in this direction have a close packing of the tertiary butyl groups. Nevertheless, this packing should be compatible with the increasing of the reorientational frequency of the fluctuations of the dipole axis, around which (C 3 0 -axis) uniaxial molecular reorientations between the three equivalent positions, and thus large thermal expansion occurs in such a direction.…”

Section: Discussionmentioning

confidence: 95%

Structure of Phase III and Polymorphism of (CH₃)₃CBr

Négrier

Barrio

Tamarit

et al. 2010

Crystal Growth & Design

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The polymorphism of 2-bromo-2-methyl-propane ((CH 3) 3 CBr) has been investigated by both thermal and X-ray powder diffraction experiments. The long time unknown structure of the low-temperature phase III has been determined by X-ray powder diffraction as orthorhombic Pmn2 1 , with lattice parameters a = 19.1350(4) Å , b = 5.7378(1) Å , and c = 10.9626(2) Å at 180 K, Z = 8 and with an asymmetric unit containing one molecule in a general position and two additional molecules placed in a mirror (Z 0 = 1 þ 1/2 þ 1/2). The phase transitions between the different phases have been characterized at normal pressure as well as at high pressures (up to 300 MPa). From the p T slopes of the two-phase coexistence lines and density measurements as a function of pressure, the volume variations at the transition points have been obtained and compared with those obtained by means of X-ray powder diffraction at normal pressure. The packing as well as the anisotropy of the intermolecular interactions have been analyzed by means of the thermal-expansion tensor and compared with tert-butyl ((CH 3) 3 CX, X = Cl, CN) related compounds.

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Section: Discussionmentioning

confidence: 95%

Structure of Phase III and Polymorphism of (CH₃)₃CBr

Négrier

Barrio

Tamarit

et al. 2010

Crystal Growth & Design

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“…A simpli®ed model was used to determine V m based on the consideration of rigid molecules and assuming that the atoms of these molecules are maintained at a constant distance. In spite of these simple assumptions, this model has been proved to be valid (Barrio et al, 1996;Tamarit, Barrio et al, 1997). The van der Waals radii and interatomic chemical bonds used have been reported previously (Tamarit, Barrio et al, 1997).…”

Section: Discussionmentioning

confidence: 97%

“…In spite of these simple assumptions, this model has been proved to be valid (Barrio et al, 1996;Tamarit, Barrio et al, 1997). The van der Waals radii and interatomic chemical bonds used have been reported previously (Tamarit, Barrio et al, 1997).…”

Section: Discussionmentioning

confidence: 97%

“…For a set of similar compounds (one of them being NPG), such a high change was initially associated with the complete breakdown of the hydrogen bonds present in the low-temperature phase II on the basis of IR spectroscopy (Benson et al, 1986). This suggestion, which was met with sharp criticism by a large number of authors, has now been refuted as a result of the study of the packing coef®cients as well as the analysis of the Raman spectra, NMR and dielectric studies of related compounds (Barrio et al, 1995(Barrio et al, , 1996Schroetter & Bougeard, 1987;Wu È r¯inger, 1993;Granzow, 1996;Tamarit, Perez-Jubindo & de la Fuente, 1997;Tamarit, Barrio et al, 1997). With respect to the ordered phase II for the substances studied in this work, we report on the anisotropy of the intermolecular interactions by means of the study of the isobaric thermal-expansion tensor in the range from 93 K up to the II-to-I phase transition of the compounds.…”

Section: Introductionmentioning

confidence: 99%

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Anisotropy of the Intermolecular Interactions from the Study of the Thermal-Expansion Tensor

Salud¹,

López²,

Tamarit³

et al. 1998

MSF

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The anisotropy of the intermolecular interactions in the low-temperature ordered phases of three chemically and structurally related compounds [neopentylglycol, (CH 3 ) 2 C(CH 2 OH) 2 , pivalic acid, (CH 3 ) 3 C(COOH), and neopentylalcohol, (CH 3 ) 3 C(CH 2 OH)], all of which display an orientationally disordered high-temperature phase, has been shown by means of the isobaric thermalexpansion tensor. The variation of the directions of the principal components of the thermal-expansion tensor as a function of temperature, as well as the variation of its principal coef®cients, is evidence of the large differences in the intermolecular interactions for each compound; or, more precisely, between the strong intermolecular hydrogen bonds and the weak van der Waals interactions. In addition, the differences in the hydrogen-bonding schemes expected a priori from the molecular structures of the studied compounds have been enhanced. Finally, the volume expansivity as well as the packing coef®cient have been analysed in the orientationally disordered high-temperature phase of each of the three compounds.

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“…The importance of hydrogen bonds in liquid aqueous media is notorious, as they determine the anomalous density behavior, solvation power, and proton transfer properties of water, , and are a fundamental ingredient for protein folding and molecular recognition . Perhaps less celebrated is the fact that hydrogen bonding is equally important also for the solid state properties of many organic systems. , For example, extensive hydrogen bonding is responsible for the large molecular dipole moments of biopolymers (e.g., DNA helices) and plays a fundamental role in the piezoelectricity and ferroelectricity of order–disorder ferroelectric materials; , the first piezoelectric material ever to be identified was in fact a hydrogen-bonded hydrate salt . If the hydrogen-bond network is dynamic, it can result in a particular type of charge transport, known as proton exchange or Grotthuss mechanism, which is for example responsible for the relatively high dc conductivity of ice as well as that of water , and of some hydrates and water clathrates, and for the conductivity enhancement of low-conductivity materials upon condensation of water vapor. , …”

Section: Introductionmentioning

confidence: 99%

Polymorphism with Conformational Isomerism and Incomplete Crystallization in Solid Ethanolamine

Romanini

Négrier

Tripathi

et al. 2019

Crystal Growth & Design

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We employ calorimetry, Rietveld refinement of X-ray powder diffraction, broadband dielectric spectroscopy and molecular dynamics simulations, to investigate the phase behavior, crystal structure, dc conductivity and dielectric response of the condensed phases of ethanolamine (EAM), an ethane derivative with two distinct hydrogen-bonding groups. EAM is found to exhibit, besides its stable crystal phase, a metastable crystalline phase obtained from the supercooled liquid phase. The metastable phase can only be maintained at low temperature; upon heating an irreversible exothermic transformation to the stable crystal structure takes place at 210 K, with a low transition enthalpy of ca. 2.4 J/g. The observed polymorphism is accompanied by differences in the molecular conformation and degree of structural order. Each EAM molecule participates in six H-bonds in both crystalline phases. While the stable phase is fully ordered, the metastable phase appears to be characterized by a statistical disorder in the position of the hydrogen atoms and thus of the intramolecular conformation and intermolecular hydrogen bonding. Our molecular dynamics simulations suggest that such disorder is dynamic in character, and allow analyzing the dynamic H-bonding motif of the metastable phase in terms of composition, length and energy of the H-bonds, and molecular conformations involved. Charge conduction is mainly ionic in both crystalline phases and exhibits the typical temperature dependence of disordered solid electrolytes, rather than crystalline ones. Dielectric characterization indicates that, upon crystallization of liquid EAM, a small fraction of the sample (approximately 5%) remains amorphous, a situation similar to that reported for other H-bonded systems such as glycerol and nbutanol.

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Packing Disordered Molecular Crystals and their Molecular Alloys

Cited by 19 publications

References 6 publications

Structure of Phase III and Polymorphism of (CH₃)₃CBr

Structure of Phase III and Polymorphism of (CH₃)₃CBr

Anisotropy of the Intermolecular Interactions from the Study of the Thermal-Expansion Tensor

Polymorphism with Conformational Isomerism and Incomplete Crystallization in Solid Ethanolamine

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Packing Disordered Molecular Crystals and their Molecular Alloys

Cited by 19 publications

References 6 publications

Structure of Phase III and Polymorphism of (CH3)3CBr

Structure of Phase III and Polymorphism of (CH3)3CBr

Anisotropy of the Intermolecular Interactions from the Study of the Thermal-Expansion Tensor

Polymorphism with Conformational Isomerism and Incomplete Crystallization in Solid Ethanolamine

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Product

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Structure of Phase III and Polymorphism of (CH₃)₃CBr

Structure of Phase III and Polymorphism of (CH₃)₃CBr